/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
 *
 *
 *
 * Written by Doug Lea and Josh Bloch with assistance from members of
 * JCP JSR-166 Expert Group and released to the public domain, as explained
 * at http://creativecommons.org/publicdomain/zero/1.0/
 */

package com.wuhan.template.utils;

import java.util.Iterator;
import java.util.Queue;

/**
 * A linear collection that supports element insertion and removal at both ends.
 * The name <i>deque</i> is short for "double ended queue" and is usually
 * pronounced "deck". Most <tt>Deque</tt> implementations place no fixed limits
 * on the number of elements they may contain, but this interface supports
 * capacity-restricted deques as well as those with no fixed size limit.
 * <p/>
 * <p/>
 * This interface defines methods to access the elements at both ends of the
 * deque. Methods are provided to insert, remove, and examine the element. Each
 * of these methods exists in two forms: one throws an exception if the
 * operation fails, the other returns a special value (either <tt>null</tt> or
 * <tt>false</tt>, depending on the operation). The latter form of the insert
 * operation is designed specifically for use with capacity-restricted
 * <tt>Deque</tt> implementations; in most implementations, insert operations
 * cannot fail.
 * <p/>
 * <p/>
 * The twelve methods described above are summarized in the following table:
 * <p/>
 * <p/>
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <tr>
 * <td></td>
 * <td ALIGN=CENTER COLSPAN = 2><b>First Element (Head)</b></td>
 * <td ALIGN=CENTER COLSPAN = 2><b>Last Element (Tail)</b></td>
 * </tr>
 * <tr>
 * <td></td>
 * <td ALIGN=CENTER><em>Throws exception</em></td>
 * <td ALIGN=CENTER><em>Special value</em></td>
 * <td ALIGN=CENTER><em>Throws exception</em></td>
 * <td ALIGN=CENTER><em>Special value</em></td>
 * </tr>
 * <tr>
 * <td><b>Insert</b></td>
 * <td>{@link #addFirst addFirst(e)}</td>
 * <td>{@link #offerFirst offerFirst(e)}</td>
 * <td>{@link #addLast addLast(e)}</td>
 * <td>{@link #offerLast offerLast(e)}</td>
 * </tr>
 * <tr>
 * <td><b>Remove</b></td>
 * <td>{@link #removeFirst removeFirst()}</td>
 * <td>{@link #pollFirst pollFirst()}</td>
 * <td>{@link #removeLast removeLast()}</td>
 * <td>{@link #pollLast pollLast()}</td>
 * </tr>
 * <tr>
 * <td><b>Examine</b></td>
 * <td>{@link #getFirst getFirst()}</td>
 * <td>{@link #peekFirst peekFirst()}</td>
 * <td>{@link #getLast getLast()}</td>
 * <td>{@link #peekLast peekLast()}</td>
 * </tr>
 * </table>
 * <p/>
 * <p/>
 * This interface extends the {@link Queue} interface. When a deque is used as a
 * queue, FIFO (First-In-First-Out) behavior results. Elements are added at the
 * end of the deque and removed from the beginning. The methods inherited from
 * the <tt>Queue</tt> interface are precisely equivalent to <tt>Deque</tt>
 * methods as indicated in the following table:
 * <p/>
 * <p/>
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <tr>
 * <td ALIGN=CENTER><b><tt>Queue</tt> Method</b></td>
 * <td ALIGN=CENTER><b>Equivalent <tt>Deque</tt> Method</b></td>
 * </tr>
 * <tr>
 * <td>{@link Queue#add add(e)}</td>
 * <td>{@link #addLast addLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link Queue#offer offer(e)}</td>
 * <td>{@link #offerLast offerLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link Queue#remove remove()}</td>
 * <td>{@link #removeFirst removeFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link Queue#poll poll()}</td>
 * <td>{@link #pollFirst pollFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link Queue#element element()}</td>
 * <td>{@link #getFirst getFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link Queue#peek peek()}</td>
 * <td>{@link #peek peekFirst()}</td>
 * </tr>
 * </table>
 * <p/>
 * <p/>
 * Deques can also be used as LIFO (Last-In-First-Out) stacks. This interface
 * should be used in preference to the legacy {@link Stack} class. When a deque
 * is used as a stack, elements are pushed and popped from the beginning of the
 * deque. Stack methods are precisely equivalent to <tt>Deque</tt> methods as
 * indicated in the table below:
 * <p/>
 * <p/>
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <tr>
 * <td ALIGN=CENTER><b>Stack Method</b></td>
 * <td ALIGN=CENTER><b>Equivalent <tt>Deque</tt> Method</b></td>
 * </tr>
 * <tr>
 * <td>{@link #push push(e)}</td>
 * <td>{@link #addFirst addFirst(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #pop pop()}</td>
 * <td>{@link #removeFirst removeFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #peek peek()}</td>
 * <td>{@link #peekFirst peekFirst()}</td>
 * </tr>
 * </table>
 * <p/>
 * <p/>
 * Note that the {@link #peek peek} method works equally well when a deque is
 * used as a queue or a stack; in either case, elements are drawn from the
 * beginning of the deque.
 * <p/>
 * <p/>
 * This interface provides two methods to remove interior elements,
 * {@link #removeFirstOccurrence removeFirstOccurrence} and
 * {@link #removeLastOccurrence removeLastOccurrence}.
 * <p/>
 * <p/>
 * Unlike the {@link List} interface, this interface does not provide support
 * for indexed access to elements.
 * <p/>
 * <p/>
 * While <tt>Deque</tt> implementations are not strictly required to prohibit
 * the insertion of null elements, they are strongly encouraged to do so. Users
 * of any <tt>Deque</tt> implementations that do allow null elements are
 * strongly encouraged <i>not</i> to take advantage of the ability to insert
 * nulls. This is so because <tt>null</tt> is used as a special return value by
 * various methods to indicated that the deque is empty.
 * <p/>
 * <p/>
 * <tt>Deque</tt> implementations generally do not define element-based versions
 * of the <tt>equals</tt> and <tt>hashCode</tt> methods, but instead inherit the
 * identity-based versions from class <tt>Object</tt>.
 * <p/>
 * <p/>
 * This interface is a member of the <a href="{@docRoot}
 * /../technotes/guides/collections/index.html"> Java Collections Framework</a>.
 *
 * @param <E> the type of elements held in this collection
 * @author Doug Lea
 * @author Josh Bloch
 * @since 1.6
 */

public interface Deque<E> extends Queue<E>
{
    /**
     * Inserts the specified element at the front of this deque if it is
     * possible to do so immediately without violating capacity restrictions.
     * When using a capacity-restricted deque, it is generally preferable to use
     * method {@link #offerFirst}.
     *
     * @param e the element to add
     * @throws IllegalStateException    if the element cannot be added at this time due to capacity
     *                                  restrictions
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    void addFirst(E e);

    /**
     * Inserts the specified element at the end of this deque if it is possible
     * to do so immediately without violating capacity restrictions. When using
     * a capacity-restricted deque, it is generally preferable to use method
     * {@link #offerLast}.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #add}.
     *
     * @param e the element to add
     * @throws IllegalStateException    if the element cannot be added at this time due to capacity
     *                                  restrictions
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    void addLast(E e);

    /**
     * Inserts the specified element at the front of this deque unless it would
     * violate capacity restrictions. When using a capacity-restricted deque,
     * this method is generally preferable to the {@link #addFirst} method,
     * which can fail to insert an element only by throwing an exception.
     *
     * @param e the element to add
     * @return <tt>true</tt> if the element was added to this deque, else
     * <tt>false</tt>
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    boolean offerFirst(E e);

    /**
     * Inserts the specified element at the end of this deque unless it would
     * violate capacity restrictions. When using a capacity-restricted deque,
     * this method is generally preferable to the {@link #addLast} method, which
     * can fail to insert an element only by throwing an exception.
     *
     * @param e the element to add
     * @return <tt>true</tt> if the element was added to this deque, else
     * <tt>false</tt>
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    boolean offerLast(E e);

    /**
     * Retrieves and removes the first element of this deque. This method
     * differs from {@link #pollFirst pollFirst} only in that it throws an
     * exception if this deque is empty.
     *
     * @return the head of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E removeFirst();

    /**
     * Retrieves and removes the last element of this deque. This method differs
     * from {@link #pollLast pollLast} only in that it throws an exception if
     * this deque is empty.
     *
     * @return the tail of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E removeLast();

    /**
     * Retrieves and removes the first element of this deque, or returns
     * <tt>null</tt> if this deque is empty.
     *
     * @return the head of this deque, or <tt>null</tt> if this deque is empty
     */
    E pollFirst();

    /**
     * Retrieves and removes the last element of this deque, or returns
     * <tt>null</tt> if this deque is empty.
     *
     * @return the tail of this deque, or <tt>null</tt> if this deque is empty
     */
    E pollLast();

    /**
     * Retrieves, but does not remove, the first element of this deque.
     * <p/>
     * This method differs from {@link #peekFirst peekFirst} only in that it
     * throws an exception if this deque is empty.
     *
     * @return the head of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E getFirst();

    /**
     * Retrieves, but does not remove, the last element of this deque. This
     * method differs from {@link #peekLast peekLast} only in that it throws an
     * exception if this deque is empty.
     *
     * @return the tail of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E getLast();

    /**
     * Retrieves, but does not remove, the first element of this deque, or
     * returns <tt>null</tt> if this deque is empty.
     *
     * @return the head of this deque, or <tt>null</tt> if this deque is empty
     */
    E peekFirst();

    /**
     * Retrieves, but does not remove, the last element of this deque, or
     * returns <tt>null</tt> if this deque is empty.
     *
     * @return the tail of this deque, or <tt>null</tt> if this deque is empty
     */
    E peekLast();

    /**
     * Removes the first occurrence of the specified element from this deque. If
     * the deque does not contain the element, it is unchanged. More formally,
     * removes the first element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt> (if such
     * an element exists). Returns <tt>true</tt> if this deque contained the
     * specified element (or equivalently, if this deque changed as a result of
     * the call).
     *
     * @param o element to be removed from this deque, if present
     * @return <tt>true</tt> if an element was removed as a result of this call
     * @throws ClassCastException   if the class of the specified element is incompatible with
     *                              this deque (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this deque does not
     *                              permit null elements (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     */
    boolean removeFirstOccurrence(Object o);

    /**
     * Removes the last occurrence of the specified element from this deque. If
     * the deque does not contain the element, it is unchanged. More formally,
     * removes the last element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt> (if such
     * an element exists). Returns <tt>true</tt> if this deque contained the
     * specified element (or equivalently, if this deque changed as a result of
     * the call).
     *
     * @param o element to be removed from this deque, if present
     * @return <tt>true</tt> if an element was removed as a result of this call
     * @throws ClassCastException   if the class of the specified element is incompatible with
     *                              this deque (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this deque does not
     *                              permit null elements (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     */
    boolean removeLastOccurrence(Object o);

    // *** Queue methods ***

    /**
     * Inserts the specified element into the queue represented by this deque
     * (in other words, at the tail of this deque) if it is possible to do so
     * immediately without violating capacity restrictions, returning
     * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
     * if no space is currently available. When using a capacity-restricted
     * deque, it is generally preferable to use {@link #offer(Object) offer}.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #addLast}.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws IllegalStateException    if the element cannot be added at this time due to capacity
     *                                  restrictions
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    boolean add(E e);

    /**
     * Inserts the specified element into the queue represented by this deque
     * (in other words, at the tail of this deque) if it is possible to do so
     * immediately without violating capacity restrictions, returning
     * <tt>true</tt> upon success and <tt>false</tt> if no space is currently
     * available. When using a capacity-restricted deque, this method is
     * generally preferable to the {@link #add} method, which can fail to insert
     * an element only by throwing an exception.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #offerLast}.
     *
     * @param e the element to add
     * @return <tt>true</tt> if the element was added to this deque, else
     * <tt>false</tt>
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    boolean offer(E e);

    /**
     * Retrieves and removes the head of the queue represented by this deque (in
     * other words, the first element of this deque). This method differs from
     * {@link #poll poll} only in that it throws an exception if this deque is
     * empty.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #removeFirst()}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E remove();

    /**
     * Retrieves and removes the head of the queue represented by this deque (in
     * other words, the first element of this deque), or returns <tt>null</tt>
     * if this deque is empty.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #pollFirst()}.
     *
     * @return the first element of this deque, or <tt>null</tt> if this deque
     * is empty
     */
    E poll();

    /**
     * Retrieves, but does not remove, the head of the queue represented by this
     * deque (in other words, the first element of this deque). This method
     * differs from {@link #peek peek} only in that it throws an exception if
     * this deque is empty.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #getFirst()}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E element();

    /**
     * Retrieves, but does not remove, the head of the queue represented by this
     * deque (in other words, the first element of this deque), or returns
     * <tt>null</tt> if this deque is empty.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #peekFirst()}.
     *
     * @return the head of the queue represented by this deque, or <tt>null</tt>
     * if this deque is empty
     */
    E peek();

    // *** Stack methods ***

    /**
     * Pushes an element onto the stack represented by this deque (in other
     * words, at the head of this deque) if it is possible to do so immediately
     * without violating capacity restrictions, returning <tt>true</tt> upon
     * success and throwing an <tt>IllegalStateException</tt> if no space is
     * currently available.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #addFirst}.
     *
     * @param e the element to push
     * @throws IllegalStateException    if the element cannot be added at this time due to capacity
     *                                  restrictions
     * @throws ClassCastException       if the class of the specified element prevents it from being
     *                                  added to this deque
     * @throws NullPointerException     if the specified element is null and this deque does not
     *                                  permit null elements
     * @throws IllegalArgumentException if some property of the specified element prevents it from
     *                                  being added to this deque
     */
    void push(E e);

    /**
     * Pops an element from the stack represented by this deque. In other words,
     * removes and returns the first element of this deque.
     * <p/>
     * <p/>
     * This method is equivalent to {@link #removeFirst()}.
     *
     * @return the element at the front of this deque (which is the top of the
     * stack represented by this deque)
     * @throws NoSuchElementException if this deque is empty
     */
    E pop();

    // *** Collection methods ***

    /**
     * Removes the first occurrence of the specified element from this deque. If
     * the deque does not contain the element, it is unchanged. More formally,
     * removes the first element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt> (if such
     * an element exists). Returns <tt>true</tt> if this deque contained the
     * specified element (or equivalently, if this deque changed as a result of
     * the call).
     * <p/>
     * <p/>
     * This method is equivalent to {@link #removeFirstOccurrence}.
     *
     * @param o element to be removed from this deque, if present
     * @return <tt>true</tt> if an element was removed as a result of this call
     * @throws ClassCastException   if the class of the specified element is incompatible with
     *                              this deque (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this deque does not
     *                              permit null elements (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     */
    boolean remove(Object o);

    /**
     * Returns <tt>true</tt> if this deque contains the specified element. More
     * formally, returns <tt>true</tt> if and only if this deque contains at
     * least one element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o element whose presence in this deque is to be tested
     * @return <tt>true</tt> if this deque contains the specified element
     * @throws ClassCastException   if the type of the specified element is incompatible with
     *                              this deque (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this deque does not
     *                              permit null elements (<a
     *                              href="Collection.html#optional-restrictions">optional</a>)
     */
    boolean contains(Object o);

    /**
     * Returns the number of elements in this deque.
     *
     * @return the number of elements in this deque
     */
    public int size();

    /**
     * Returns an iterator over the elements in this deque in proper sequence.
     * The elements will be returned in order from first (head) to last (tail).
     *
     * @return an iterator over the elements in this deque in proper sequence
     */
    Iterator<E> iterator();

    /**
     * Returns an iterator over the elements in this deque in reverse sequential
     * order. The elements will be returned in order from last (tail) to first
     * (head).
     *
     * @return an iterator over the elements in this deque in reverse sequence
     */
    Iterator<E> descendingIterator();

}
